Effects of polar group incorporation on crazing of glassy polymers: Styrene–acrylonitrile copolymer and a dicyano bisphenol polycarbonate

The degree of swelling and attendant reduction in the glass transition temperature have been determined for a 70% styrene–30% acrylonitrile copolymer in a large number of organic liquids. The critical strain ϵ_c for crazing or cracking has been determined also in air and in each agent. Limited crazing data have been obtained also on a dicyano bisphenol polycarbonate in which the CN groups take the place of the methyl groups in bisphenol A (BPA) polycarbonate. The two resins are compared with polystyrene and BPA polycarbonate, respectively, in terms of crazing resistance, swelling, and other properties. In both systems CN incorporation raises ϵ_c (air) and reduces susceptibility to liquids of low solubility parameter δ; T_g and shear yield stress are raised in the polycarbonate but not in the styrene system. The volume efficiency of CN in raising ϵ_c (air) is greater in the polycarbonate system than the styrene system; for the rise in polymer solubility parameter, CN efficiency is apparently reversed. These changes are discussed in terms of the differences in molecular architecture of the two systems. For glassy polymers, ϵ_c (air) is shown to depend in semiquantitative fashion on polymer T_g, δ, and resistance to shear deformation.